Liquid Crystal Display Device

ABSTRACT

A liquid crystal display device comprising a liquid crystal display panel, a backlight and a heat sink member is disclosed. The backlight comprises a light-guiding plate disposed on one principal surface side of the liquid crystal display panel, LED light sources disposed on an end surface of the light-guiding plate, a mounting board for mounting the LED light sources thereon and a thermally conductive member connected to the mounting board. The heat sink member is connected to the mounting board through the thermally conductive member.

BACKGROUND OF THE INVENTION

1. Field of the Invention

The present invention relates to a liquid crystal display devicecomprising a liquid crystal display panel and a backlight, and inparticular, to a liquid crystal display device which utilizes a lightemitting diode (hereinafter simply referred to as “LED”) as a lightsource.

2. Description of Related Art

Among conventional liquid crystal display devices, transmissive-type andtransflective-type liquid crystal display devices are each provided witha liquid crystal display panel and a backlight for supplying lighttransmitting through the liquid crystal panel.

Generally, a backlight includes a light source and a light-guidingplate, and a small fluorescent tube called CCFL (cold cathodefluorescent tube) is used as the light source. One principal surface ofthe light-guiding plate is disposed so as to correspond to a displayarea of the liquid crystal display panel, and a diffusion area fordiffusing and reflecting light toward the surface side is provided onthe other principal surface thereof (referred to as “outer surface”)opposite to the aforementioned principal surface.

The CCFL light source is disposed at an end surface of the light-guidingplate so that light of CCFL incident on the end surface of thelight-guiding plate is transmitted inside the light-guiding plate, andis diffused/reflected on the outer surface side of the light-guidingplate to be directed from the surface of the light-guiding plate towardthe liquid crystal panel. Thus, the light source is converted from alinear light source into a homogeneous planar light source to beutilized as the light source for the liquid crystal device.

However, this CCFL light source uses Hg (mercury) encapsulated in adischarge tube that emits ultraviolet rays when excited by electricaldischarge, which strike the fluorescent substance on the CCFL tube wallto be converted into visible light rays.

For this reason, when considering the environmental aspect, using analternative light source is required for restricting the use ofhazardous mercury.

In addition, in order to illuminate the CCFL, a high-voltage andhigh-frequency switching circuit is necessary. However, since thiscauses high frequency noise, not only noise prevention is additionallyrequired, but also problems such as slow light-up under low temperature,low luminous efficiency and the like are prone to arise.

In the meantime, as a new light source, an LED backlight utilizing alight emitting diode module (LED light source) accommodating LED chipscharacterized by a point light source has been developed.

With demands for lower price, higher luminous efficiency andenvironmental regulations, this backlight utilizing the LED light sourceis becoming to be widely used as the backlight for liquid crystaldisplay panels.

At the same time, with increased brightness and display area of liquidcrystal display devices, the demand for providing a plurality of LEDlight sources is increasingly high.

Accordingly, when an LED backlight is used for a high brightness, largesize liquid crystal display panel, the LED light source, which is apoint light source, needs to be converted into a planar light sourcethat emits light rays evenly (light source that has been converted intoeven light rays at the light-emitting surface of the light-guidingplate). For this reason, it is necessary to adjust the material andstructure of the diffusion area of the outer surface of thelight-guiding plate, and to dispose the LED light source at an optimumposition in accordance with the orientation of the LED light source.

However, one problem here is that the temperature of the LED and itsperipheral regions rises due to heat generated from the LED chip,leading to decrease in luminous efficiency and life of the LED lightsource.

Therefore, in a liquid crystal display device provided with a LEDbacklight, reduction of heat storage in the mounting board on which theLED light source is mounted and suppression of temperature rise in theLED light source are required.

SUMMARY OF THE INVENTION

A liquid crystal display device according to the present inventioncomprises a liquid crystal display panel including a display pixel area,a backlight and a heat sink member. The backlight includes alight-guiding plate disposed on one principal surface of the liquidcrystal panel so as to correspond to the foregoing display pixel area,LED light sources arranged at an end portion of the light-guiding plate,a mounting board on which the LED light sources are mounted, and athermally conductive member connected to the mounting board. The heatsink member is connected to the mounting board through the thermallyconductive member.

Advantages, features and effects of the present invention will beapparent from the following description of preferred embodiments withreference to the accompanying drawings.

BRIEF DESCRIPTION OF THE DRAWINGS

FIG. 1 is a cross-sectional view of a liquid crystal display deviceaccording to one embodiment of the present invention.

FIG. 2 is a schematic perspective view of a liquid crystal displaydevice according to the present invention.

FIG. 3 is a cross-sectional view showing the structure of a liquidcrystal panel used for a liquid crystal display device according to thepresent invention.

FIG. 4 is a schematic perspective view of a mounting board on which anLED light source is mounted viewed from the LED mounting surface side.

FIG. 5 is a schematic perspective view of the mounting board on which anLED light source is mounted viewed from the rear surface side.

FIG. 6 is a schematic cross-sectional view of a mounting board on whichan LED light source according to the present invention is mounted.

FIG. 7 is an enlarged view of the part A of FIG. 6.

FIG. 8 is a schematic perspective view of an LED light source arrayincluding a plurality of LED light sources mounted on a mounting board.

FIG. 9 is a schematic view showing the structure of an LED light source.

FIG. 10 is a perspective view of an L-shaped thermally conductivemember.

FIG. 11A is a schematic cross-sectional view of a liquid crystal displaydevice according to another embodiment of the present invention.

FIG. 11B is a partially enlarged view of FIG. 11A.

FIG. 12 is a schematic cross-sectional view of a liquid crystal displaydevice according to still another embodiment of the present invention.

FIG. 13 is a perspective view of a second thermally conductive member.

FIG. 14 is a schematic perspective view of an LED light source array towhich the second thermally conductive member is press fitted.

FIG. 15 is a schematic cross-sectional view of a liquid crystal displaydevice according to yet another embodiment of the present invention.

FIGS. 16 (a)-16(c) are perspective views of thermally conductive memberseach having a U-shaped cross section used for the liquid crystal displaydevice shown in FIG. 15.

FIGS. 17 (a)-17(c) are perspective views of metal cases used for therespective thermally conductive members each having a U-shaped crosssection.

FIG. 18 is a schematic cross-sectional view of a liquid crystal displaydevice according to still another embodiment of the present invention.

FIG. 19 is a schematic cross-sectional view of a liquid crystal displaydevice according to yet another embodiment of the present invention.

FIG. 20 is a schematic perspective view of an LED light source arrayused for the liquid crystal display device of FIG. 19.

FIG. 21 is a schematic perspective view of a thermally conductive memberused for the liquid crystal display device of FIG. 19.

DETAILED DESCRIPTION OF PREFERRED EMBODIMENTS

FIG. 1 is a schematic cross-sectional view of a liquid crystal displaydevice according to the present invention, and FIG. 2 is a perspectiveview of the liquid crystal display device. FIG. 3 is a cross-sectionalview of a liquid crystal display panel used for a liquid crystal displaydevice according to the present invention.

This liquid crystal display device is composed mainly of a passive-typeliquid crystal panel 1, a backlight BL including a light-guiding plate 3and a LED light source 2, and an upper housing member 4 and a lowerhousing member 5 for protecting the liquid crystal panel 1 and thebacklight BL.

The upper housing member 4 is provided for protecting an outerperipheral area of the liquid crystal panel 1. The lower housing member5 protects the backlight BL, as well as functions as a heat sink memberfor dissipating heat generated from the LED light sources 2 of thebacklight BL to the outside. In this case, the lower housing member 5 isreferred to as “heat sink member 5” for its heat dissipating function.

<Liquid Crystal Panel>

The liquid crystal panel 1 comprises, as shown in FIG. 3, an uppertransparent substrate 12 as a substrate of one side, and a lowertransparent substrate 11 as a substrate of another side, a liquidcrystal layer 13 interposed between the both transparent substrates 11,12. The liquid crystal layer 13 is surrounded by a sealing section 14.

In addition, display electrodes 15, an alignment film and the like thatare not shown are formed on the interior surface of the lowertransparent substrate 11, and display electrodes 16, an alignment filmand the like are also formed on the interior surface of the uppertransparent substrate 12.

These display electrodes 15 of the lower transparent substrate 11 andthe display electrodes 16 of the upper transparent substrate 12constitute a plurality of pixel areas aligned in the form of a matrix,and the plurality of pixel areas form a display pixel area.

In addition, the lower transparent substrate 11 and the uppertransparent substrate 12 are each provided with a polarization plate, aretardation film, a diffusion film and the like according to need,although they are not shown in the drawings.

Meanwhile, when this liquid crystal display device is a transmissiveliquid crystal display device, usually, the display electrodes 15, 16are composed of transparent electrodes, and the display pixel areatransmits light from the backlight BL to the display surface side.

When it is a transflective liquid crystal display device, the displaypixel area includes a partially light reflective area comprising areflective metal film, and a partially light transmissive area thatpermits light from the backlight BL to penetrate.

In this transflective liquid crystal display device, external lightentering from the display area side is reflected at the light reflectivearea of the display pixel area to be returned to the display area side,and light of the backlight BL is transmitted at the light transmissivearea.

This structure enables display in the reflective mode when the externallight is intense, and display in the transmissive mode when the externallight is weak.

In addition, in order to accomplish color display, it is possible toprovide a color filter in the display pixel area of either the lowertransparent substrate 11 or the upper transparent substrate 12.

The liquid crystal display device according to the present invention mayinclude switching devices formed in the respective pixel areas of eitherthe lower transparent substrate 11 or the upper transparent substrate 12so as to control display for each pixel area.

Moreover, it is also possible to provide a wiring pattern at theperiphery the display pixel area of either of the lower and uppertransparent substrates 11, 12, for example, the upper transparentsubstrate 12, which is electrically connected to display electrodes 16,the aforementioned switching devices formed in the respective pixelareas and the like so that an active type liquid crystal display panelcan be constructed by providing the wiring pattern with a drive circuitfor supplying a predetermined signal and a predetermined voltage and aninput terminal for connection to an external drive circuit.

The display electrodes of the substrate that is not provided with thewiring pattern, for example, the display electrodes 15 of the lowertransparent substrate 11 may be electrically connected to the wiringpattern of the upper transparent substrate 12 through a conductivefiller inside the sealing section 14 disposed at the periphery betweenboth substrates 11 and 12.

The material for the lower transparent substrate 11 and the uppertransparent substrate 12 may be glass, translucent plastic or the like.The display electrodes 15, 16 are formed using a transparent conductivematerial such as ITO, tin oxide or the like. The reflective metal filmconstituting the light reflection area is made of aluminum, titanium orthe like. In addition, the alignment film is made of rubbed polyimide.When color filters are provided, resin to which dyes and pigments areadded is used to form red, green, and blue filters for each pixel area.It is also possible to provide black resin between the respectivefilters and around the pixel areas for a light-shielding purpose.

These lower transparent substrate 11 and upper transparent substrate 12are joined through the sealing section 14 by pressure, and a liquidcrystal material including nematic liquid crystal or the like isinjected from an opening provided in the sealing section 14, and thenthe opening is sealed.

The joining is carried out so that the display electrodes 15 and 16aligned on the transparent substrates 11 and 12, respectively, aretwo-dimensionally cross each other. An area at which a display electrode15 and a display electrode 16 are opposed to each other forms a pixelarea, and an assembly of the pixel areas forms a display pixel area.

The passive type liquid crystal display panel 1 is constructed in theforegoing manner.

<Backlight>

A backlight BL is disposed outside (in the lower side in FIG. 1) of thelower transparent substrate 11 of the liquid crystal display panel 1.

As shown in FIG. 1, the backlight BL is provided with an LED lightsource 2, a light-guiding plate 3, a lens sheet 3 a, a diffusion sheet 3b, a reflection sheet 3 c, an elongated mounting board 21 disposedgenerally in parallel to an end surface of the light-guiding plate 3,and a thermally conductive sheet 31 as a thermally conductive member.The thermally conductive sheet 31 is in tight attachment to a heat sinkmember 5 and the mounting board 21.

The thermal conductivity of the thermally conductive sheet 31 ispreferably at least 0.3 W/(m·K), and more preferably, greater than thethermal conductivity of the mounting board 21. For example, when themounting board 21 comprises a glass epoxy substrate, the thermallyconductive sheet 31 preferably has a thermal conductivity greater thanthe thermal conductivity 0.45 W/(m·K) of the glass epoxy substrate.

Here, the thermally conductive sheet 31 is preferably made of softrubber so that it excludes air (its thermal conductivity is 0.024W/(m·K)) from its contact surface with the heat sink member 5 or itscontact surface with the mounting board 21. Specifically, the thermallyconductive sheet 31 preferably has a JIS-A rubber hardness of 5-60degree (defined in JIS-K6253). With a JIS-A rubber hardness lower than5, the thermally conductive sheet 31 is too soft to keep the position ofitself stable. With a JIS-A rubber hardness greater than 60, thethermally conductive sheet 31 is so hard that its adhesion to themounting board 21 and the heat sink member 5 weakens and fails toeffectively exclude air from the aforementioned contact surfaces.

The light-guiding plate 3 has a shape corresponding to the display areaof the liquid crystal panel 1. One principal surface of thelight-guiding plate 3 (the surface from which light is emitted) isdisposed so as to be opposed to the lower transparent substrate 11.

The light-guiding plate 3 comprises a transparent resin plate. A lightdiffusing material may be included in the resin component. A lens sheet3 a and a diffusion sheet 3 b are disposed on the one principal surfaceof the light-guiding plate 3, and on another principal surface (referredto as “outer surface”) of the light-guiding plate 3, a reflection sheet3 c for radiating light that propagates inside the light-guiding plate 3to the side of the one principal surface is disposed.

Instead of the reflection sheet 3 c, grooves for directlydiffusing/reflecting light, or a film having a diffusing/reflectingfunction may be formed on the outer surface of the light-guiding plate3.

In addition, the reflection sheet 3 c may be formed on three of the fourend surfaces of the light-guiding plate 3 excluding the end surface onwhich the LED light sources 2 are disposed.

The LED light sources 2 are mounted on the mounting board 21 as shown inFIGS. 4, 6 and 8.

The LED light source 2 whose cross-section is shown in FIG. 9 comprisesan LED chip 23 a including a light-emitting section made of asemiconductor material, an anode electrode and a cathode electrode, andan LED container 23 b made of a heat-resistant resin material, a ceramicmaterial or the like that has a cavity 23 d for accommodating the LEDchip 23 a.

This LED container 23 b of the LED light source 2 has a light-emittingsurface, a back surface opposed to the mounting board 21, and four sidesurfaces, and the light-emitting surface of the LED container 23 b isdisposed so as to be in tight attachment to the end surface of thelight-guiding plate 3 as shown in FIG. 1.

The cavity 23 d is formed on the light-emitting surface of the LEDcontainer 23 b, and the LED chip 23 a is disposed on a bottom part ofthe cavity 23 d.

The anode electrode and cathode electrode of the LED chip 23 a areelectrically connected to terminal portions 23 c formed over sidesurfaces and the back surface of the LED container 23 b.

Meanwhile, a reflective coating may be applied to the inner wall surfaceof the cavity 23 d. Also, the interior of the cavity 23 d may be filledwith a translucent resin so as to cover the LED chip 23 a. When theinterior of the cavity 23 d is filled with a translucent resin, thelight-emitting surface of the LED container 23 b corresponds to thesurface of the translucent resin. When the cavity is not filled with atranslucent resin, the light-emitting surface of the LED container 23 bcorresponds to an opening of the cavity 23 d.

A plurality of the LED light sources 2 with the structure describedabove are mounted in a linear arrangement with intervals therebetween onthe mounting board 21 with an elongated shape as shown in FIG. 8. Theassembly including a plurality of mounted LED light sources 2 and themounting board 21 is referred to as “LED light source array”.

The mounting board 21 comprises a glass fabric-based epoxy resinsubstrate or a ceramic substrate.

On the LED-mounting surface of the mounting board 21, there are provideda mounting metal film 22 for mounting the LED light sources 2, a metaldriving wiring 24 for supplying driving current to the LED chips 23 aand a metal film pattern 25 disposed being spaced apart from the metaldriving wiring 24.

In addition, on the surface opposite to the LED-mounting surface, thatis, the back surface of the substrate, a heat dissipating metal film 26is formed to cover generally the entire surface as shown in FIG. 5.

Moreover, a plurality of metal via hole conductors 27 for connecting themetal mounting film 22 and the heat dissipating metal film 26 are formedin the thickness direction of the mounting board 21.

Terminal portions 23 c of the LED light sources 2 are connected to themetal driving wiring 24 through a conductive bonding member 28comprising solder or the like.

The metal mounting film 22, the metal driving wiring 24, the metal filmpattern 25, the heat dissipating metal film 26, and the metal via holeconductors 27 respectively are formed using copper or a copper-basedmetal material (copper material, copper plating or the like). A part ofthe metal driving wiring 24, metal mounting film 22, heat dissipatingmetal film 26 and metal via hole conductors 27 are covered with solder(referred to as “heat dissipating metal film 28”) as shown in FIG. 7,which is an enlarged view of the circled region A in FIG. 6.

The surface of the metal film pattern 25 is covered with a resin resistfilm 29. When this resist film 29 is white, light leaking from the LEDlight sources 2 can be efficiently supplied to the light-guiding plate3.

<Heat Dissipating Structure>

Now, the structure for dissipating heat generated from the LED lightsources 2 is described.

Upon driving the backlight BL (lighting up of the LED light sources 2)of the liquid crystal display device, heat is generated accompanying thelight emission.

Heat generated from the LED chips 23 a inside the LED light sources 2needs to be transferred through the LED containers 23 b and the mountingboard 21 to a member having a wider area, and dissipated to the outsideair from the member.

In order to accomplish such heat dissipation, the back surface of themounting board 21 on which the LED light sources 2 are mounted isconnected to the heat sink member 5, which is a metallic plate, throughthe thermally conductive sheet 31. This heat sink member 5 is bent so asto be opposed to the outer surface of the light-guiding plate 3, theback surface of the mounting board 21 and a side surface of the mountingboard 21.

The heat sink member 5 may be provided with thermally conductiveapertures in a region opposed to the outer surface of the light-guidingplate 3 for increasing contact with the outside air according to need.

The heat sink member 5 is in tight attachment to the heat dissipatingmetal film 26 of the mounting board 21 through the thermally conductivesheet 31 as shown in FIG. 1.

FIG. 10 shows a perspective view of this thermally conductive sheet 31.

The thermally conductive sheet 31 covers the back surface of themounting board 21, as well as includes an extended portion 31 a thatcovers at least one of side surfaces connecting the back surface to theforegoing LED-mounting surface, and the extended portion 31 a is alsoconnected to the foregoing heat sink member 5 (See FIG. 1).

This thermally conductive sheet 31 and the heat sink member 5 are insurface contact with each other.

Since this thermally conductive sheet 31 is made of soft rubber, evenwhen minute irregularities are present on the surfaces of the mountingboard 21 and the heat sink member 5, interposition of air gaps betweenthe mounting board 21 and the thermally conductive sheet 31 and betweenthe thermally conductive sheet 31 and the heat sink member 5 isrestricted. As a result, the thermally conductive sheet 31 and the heatsink member 5, and the mounting board 21 and the heat sink member 5,respectively, are brought into surface contact with each other in goodcondition. This structure transfers the heat generated from the LEDlight sources 2 from the LED container 23 b to the mounting board 21,and stably conducts to the heat sink member 5 through the thermallyconductive sheet 31. This makes it possible to transfer the heatgenerated from the LED chips 23 to the heat sink member 5, and as aresult, to decrease the temperature of the LED light sources 2 andregions around them.

In particular, because of the arrangement in which the thermallyconductive sheet 31 is in contact with the back surface and an endsurface of the mounting board 21, heat can be transferred also from theend surface of the mounting board 21 through the thermally conductivesheet 31. Accordingly, the heat stored in the mounting board 21 can betransferred efficiently to the heat sink member 5.

Here, as shown in FIG. 10, the thermally conductive sheet 31 is designedso that the thickness thereof before it is interposed between themounting board 21 and the heat sink member 5 is slightly greater thanthe distance between the mounting board 21 and the heat sink member 5.Because of this, the thermally conductive sheet 31 is pressed stronglyby the mounting board 21 and the heat sink member 5 when the thermallyconductive sheet 31 is interposed between the mounting board 21 and theheat sink member 5, which favorably restricts gap generation at contactsurfaces between the mounting board 21 and the heat sink member 5.

In addition, it is preferable to planarize the end surface of themounting board 21 with which the thermally conductive sheet 31 isbrought into contact by grinding and polishing. This allows thethermally conductive sheet 31 to attach tightly to the end surface ofthe mounting board 21 in good condition.

In particular, since glass and plastic chippings produced in edge lineportions of the end surface of the mounting board 21 can be removed bypolishing, it is possible to effectively prevent air gaps fromgenerating between the mounting board 21 and the thermally conductivesheet 31, and to dissipate heat efficiently.

Moreover, it is also possible to preclude light blocking effect due tothe adherence of glass and plastic chippings produced from the cutsurface of the mounting board 21 to the LED light sources 2, so thatlight of the light sources 2 can be utilized efficiently.

Now, the structure of another thermally conductive member which iseffectively used together with the thermally conductive sheet 31 isdescribed.

FIG. 11A shows a schematic cross-sectional view of a liquid crystaldisplay device according to the present invention, and FIG. 11B is apartially enlarged cross-sectional view of the device in FIG. 11A. Thesame elements as in FIG. 1 are denoted by the same reference numerals.Features that are different from those in FIG. 1 are mainly describedbelow.

Even though the thermally conductive sheet 31 is made of a soft rubbersheet material and held between the mounting board 21 and the heat sinkmember 5 in a pressure contacted manner, air gaps might be generated atcontact surfaces between the mounting board 21 and the thermallyconductive sheet 31 and between the thermally conductive sheet 31 andthe heat sink member 5.

This is because the contact surfaces at which the mounting board 21 andthe heat sink member 5 are in contact with the thermally conductivesheet 31 are not completely smooth surfaces but inevitably includeminute irregularities, and the holding condition of the thermallyconductive sheet 31 is subject to changes due to impact or the like fromthe outside.

Therefore, in order to prevent air gaps from generating, as shown inFIG. 11B, an adhesive agent 17 with high fluidity or a fluid 17 withlarge thermal conductivity and low fluidity is interposed between thethermally conductive sheet 31 and the mounting board 21 and between thethermally conductive sheet 31 and the heat sink member 5.

When the thermally conductive sheet 31 and the mounting board 21, andthe thermally conductive sheet 31 and the heat sink member 5 are securedto each other with use of the adhesive agent 17 with high fluidity, airgap generation is further suppressed, so that the heat of the lightsources 2 can be easily transferred to the heat sink member 5.

As the adhesive agent 17 with high fluidity, for example, siliconeadhesives (such as SE9176L, an adhesive agent produced by Dow CorningToray Silicone Co., Ltd.) may be used.

The adhesive agent 17 is used for bonding the thermally conductive sheet31 and the heat sink member 5 together by being stably interposedtherebetween, and therefore, high fluidity is required for the adhesive.Specifically, the viscosity before curing is preferably 2-20 Pa·S.Meanwhile, this adhesive agent is preferably of a type that hardens atroom temperature.

When the viscosity of the adhesive agent 17 before curing is less than2, the adhesive agent 17 flows out, causing bonding strength to bedecreased. When the viscosity of the adhesive agent 17 before curingexceeds 20, it fails to be stably filled between the mounting board 21and the heat sink member 5, and as a result, they are bonded togetherwith trapping air therebetween.

The fluid 17 with low fluidity comprises, for example, a silicone oilcomponent and ceramic fine particles with large thermal conductivity(which is referred to as “thermally conductive compound”).

Here, a bonding function is not particularly required for the fluid, butexpected only to suppress formation of air gaps between the mountingboard 21 and the thermally conductive member 31, and between thethermally conductive member 31 and the heat sink member 5. For thispurpose, oil components in the form of paste or grease may be recited.This fluid preferably has quite low fluidity, that is, hardly flows,unlike the adhesive agent.

Because of the presence of the fluid 17, minute irregularities on themounting board 21 and the heat sink member 5 are impregnated with theoil component of the fluid 17, thereby eliminating minute air gaps. Thisallows heat to be transferred efficiently from the mounting board 21 tothe heat sink member 5 through the thermally conductive sheet 31.

Accordingly, the heat generated at the light sources 2 is effectivelydissipated to the outside, and becomes less likely to be stored in theLED light sources 2 and mounting board 21. As a result, temperature risein the LED light sources 2 and regions around them can be effectivelysuppressed.

Still another member that is favorably used with the thermallyconductive sheet 31 will be described below.

FIG. 12 shows a schematic cross-sectional view of a liquid crystaldisplay device according to another embodiment of the present invention.The same elements as in FIG. 1 are denoted by the same referencenumerals. Features that are different from those in FIG. 1 are mainlydescribed below.

In this embodiment, a thermally conductive member 20 is disposed beingin contact with a surface of a mounting board 21 on which a LED lightsource 2 is mounted.

FIG. 13 shows a perspective view of the thermally conductive member 20.FIG. 14 shows a perspective view of parts including a mounting board 21and the LED light sources 2 mounted thereon, and the thermallyconductive member 20 to be assembled thereto.

The thermally conductive member 20 has an elongated shape almostcorresponding to the shape of the mounting board 21, and has window-likeopening portions 20 a for accommodating the LED light sources 2 mountedon the mounting board 21.

As shown in FIG. 14, the thermally conductive member 20 with aconfiguration mentioned-above is disposed on the LED-mounting surface ofthe mounting board 21. This is accomplished by placing the LED lightsources 2 that have been mounted on the mounting board 21 at the openingportions 20 a and pressing them into the opening portions 20 a.

The thermally conductive member 20 is held between the mounting board 21and the end surface on the light incident surface side of thelight-guiding plate 3 as shown FIG. 12.

Since there is the thermally conductive member 20 substantially presentaround the light sources 2, most of the heat emitted from the LED lightsources 2 to regions around the LED light sources 2 can be transferredto the heat sink member 5 through the thermally conductive member 20.

In particular, since the heat of the LED light sources 2 is rapidlytransferred from the terminal portions 23 c formed on the LED container23 b containing the LED through the metal wiring 24 formed on themounting board 21, when the thermoconductive member 20 is brought intodirect contact with electrode portions of the mounting board 21 as wellas with the terminal portions 23 c, the heat dissipating effect isfurther enhanced.

In addition, as shown in FIG. 12, because an end surface of thethermally conductive member 20 is in contact with the heat sink member5, heat conduction from the thermally conductive member 20 to the heatsink member 5 is effectively accomplished through such a contactsurface.

Accordingly, the heat generated at the LED light sources 2 iseffectively dissipated to the outside, and becomes less likely to bestored in the LED light sources 2 and the mounting board 21, so thattemperature rise in the LED light sources 2 or regions around them canbe effectively suppressed.

Now, a description will be given to the thicknesses of the thermallyconductive member 20 and the thermally conductive sheet 31.

It is important that the thickness of the thermally conductive member 20at a stage before it is interposed between the mounting board 21 and thelight-guiding plate 3 is slightly greater than the designed distancebetween the mounting board 21 and the light-guiding plate 3, in otherwords, the mounting height of the LED light source 2.

In addition, the thickness of the thermally conductive sheet 31 at astage before it is interposed between the mounting board 21 and the heatsink member 5 should be slightly greater than the designed distancebetween the mounting board 21 and the heat sink member 5.

Since the both of the thermally conductive members 20 and 31 are made ofsoft rubber, when the thicknesses are set as above, the mounting board21 with the LED light sources 2 mounted thereon is held between thelight-guiding plate 3 and the heat sink member 5 in a pressure contactedmanner, so that the mounting board 21 can be securely maintained.

Moreover, even when minute irregularities are present in the end surfaceof the light-guiding plate 3, the front and back surfaces of themounting board 21 and the surface of the heat sink member 5, such minuteirregularities are absorbed because of the rubber elasticity of thethermally conductive members 20, 31.

Accordingly, very few air gaps are present at the contact surfacesbetween the light-guiding plate 3 and the thermally conductive member20, between the mounting board 21 and the thermally conductive sheet 31,and between the thermally conductive members 21, 30 and the heat sinkmember 5, and therefore, thermal conduction properties at these contactsurfaces can be maintained to be high.

In addition, by the use of soft rubber for the thermally conductivemembers 20, 31, even when external impact is applied to the liquidcrystal display device, the impact can be absorbed by the thermallyconductive members 20, 31. Accordingly, the impact is prevented frompropagating directly to the mounting board 21. As a result, displacementof the mounting board 21, breakage of the mounting board 21 itself, ordetachment of the LED light sources 2 from the mounting board 21 nolonger occurs.

FIG. 15 shows a schematic cross-sectional view of a liquid crystaldisplay device according to still another embodiment of the presentinvention. The same elements as in FIG. 1 are denoted by the samereference numerals. Features that are different from those in FIG. 1 aremainly described below.

In this embodiment, a thermally conductive member 32 which covers thefront and back surfaces of the mounting board 21 is provided.

FIG. 16 shows an example of the thermally conductive member 32 in aperspective view.

The thermally conductive member 32 comprises, as shown in FIG. 16( a), afirst portion 32 a held between the mounting board 21 and the heat sinkmember 5, a second portion 32 b held between the mounting board 21 andthe light-guiding plate 3 and a third portion 32 c that connects thefirst portion 32 a and second portion 32 b, and covers at least one ofthe side surfaces of the mounting board 21.

The second portion 32 b is provided with a plurality of opening portions32 d at positions corresponding to the LED light sources 2 mounted onthe mounting board 21.

The opening portions 32 d are open on the upper side. Placing themounting board 21 on such a thermally conductive member 32 may beaccomplished by press fitting it from the upper side of the gap betweenthe first portion 32 a and the second portion 32 b downward with the LEDlight sources 2 being positioned at the opening portions 32 d.

Here, it is preferable to interpose the aforementioned adhesive agent 17with high fluidity or a fluid 17 with low fluidity between the thermallyconductive member 32 and the mounting board 21, between the thermallyconductive member 32 and the heat sink member 5, and between the heatsink member 5 and the light-guiding plate 3 so as to improve the thermalconduction.

FIGS. 16 (b), 16 (c) show other examples of the thermally conductivemember 32.

FIG. 16( b) shows an example in which opening portions 32 d formed in asecond portion 32 b so as to correspond to the LED light sources 2 havewindow-like shapes.

In this case, since the thermally conductive member 32 is substantiallypresent in four surfaces surrounding the LED light sources 2, most ofthe heat emitted from regions around the LED light sources 2 can betransferred through the thermally conductive member 32 to thelight-guiding plate 3 and the heat sink member 5.

Meanwhile, the placement of the mounting board 21 on the thermallyconductive member 32 may be accomplished such that with the gap betweenthe first portion 32 a and the second portion 32 b expanded from theupper side, the mounting board 21 is inserted from the upper side.

In addition, the thermally conductive member 32 may be U-shaped incross-section as shown in FIG. 16( c) so that it is in contact with thefront surface, the back surface and the end surface of the mountingboard 21.

The thermally conductive member 32 in FIG. 16( c) includes a forthportion 32 e at a position opposed to a second portion 32 b and anopening portion 32 d where LED light sources 2 are exposed so as to forma configuration corresponding to the cross-sectional shape of themounting board 21.

In this case, the mounting board 21 is laterally inserted into thethermally conductive member 32 with a U-shaped cross section.

Meanwhile, the placement of the mounting board 21 on the thermallyconductive member 32 is accomplished such that with the opening portion32 d formed in the second portion 32 b vertically opened, the mountingboard 21 is introduced. Or, the mounting board 21 may be press fit froma lateral side of the thermally conductive member 32.

Since substantially the four surfaces of the mounting board 21 arecovered by the thermally conductive member 32 in the structure in FIG.16( c), thermal conductive efficiency can be improved.

In addition, it is possible to press the thermally conductive member 32and a side surface of the mounting board 21 from the upper side by aprojected portion 4 a provided in the housing 4 of the liquid crystaldisplay device (See FIG. 15) so that the thermally conductive member 32is held between the housing 4 and the heat sink member 5. Since themounting board 21 is covered by the thermally conductive member 32 atfour surfaces thereof, it exhibits excellent heat dissipation and impactresistance.

Now, a description will be given to thickness of the thermallyconductive member 32. Since the thermally conductive member 32 isintended to hold the mounting board 21 and the heat sink member 5 in apressure contacting manner, it is preferable to design the outerdimensions of the thermally conductive member 32 to be somewhat largerthan the inner dimensions of the heat sink member 5.

Because the thermally conductive member 32 is made of a soft rubbersheet, minute irregularities on the surfaces of the mounting board 21and the heat sink member 5 are absorbed, so that the mounting board 21and the thermally conductive member 32, and the thermal conductivemember 32 and the heat sink member 5 can be brought into surface contactwith each other almost free from interposition of air gaps therebetween.

Further, there may be cases where a curved surface (R) is formed at aninner corner region of the heat sink member 5 that is in contact withthe outer surface of the thermally conductive member 32 while the metalbending or the metal pressing process. However, gaps between thethermally conductive member 32 and the heat sink member 5 that arecreated by the curved surface are filled with the thermally conductivemember 32 by the deformation of the thermally conductive member 32.

If the gaps cannot be filled with the thermally conductive member 32,the curved surface R can be removed by C-chamfering an outer cornerregion of the thermally conductive member 32 in contact with the innercurved region, so that the adhesion between the thermally conductivemember 32 and the heat sink member 5 can be further improved.

It is also possible to attach a metal case 33 described below to theouter surfaces of the thermally conductive member 32 described above.

FIGS. 17( a)-17(c) are perspective views showing the configurations of ametal case 33 as a heat sink member enclosing the thermally conductivemember 32.

Outer surfaces of the foregoing thermally conductive member 32 arecovered with these metal cases 33.

The thermally conductive member 32 and the metal case 33 are tightlyattached to each other at contact surfaces. Similarly to the thermallyconductive member 32, the metal case 33 is provided with cutout portions33 a at which the light-emitting surfaces of the light sources 2 areexposed.

Meanwhile, the metal case 33 has an effect to improve the LED lightsource utilizing efficiency. Specifically, there are light rays whichare not directed to the side of the liquid crystal panel 1 from thelight-guiding plate 3 after entering the light-guiding plate 3 from theLED light source 2, but are reflected at a reflection plate R made ofmetal provided at an end surface of the light-guiding plate 3 to returnto an end surface side of the LED light source 2 (See FIG. 15).

In such a case, if the thermally conductive member 32 is disposed at theend surface of the light-guiding plate 3, the thermally conductivemember 32 with a gray or black color absorbs such light rays, causingloss of light.

Therefore, by disposing the metal case 33 on the outer surfaces of thethermally conductive member 32, light rays can be returned to thelight-guiding plate 3 by the metal case 33, so that light is efficientlyutilized.

The means for reflecting light rays that are coming back is not limitedto the metal case 33, but may be other light reflective members orsheets disposed at predetermined regions of the thermally conductivemember 32 for that purpose.

While the metal case 33 is formed by metal processing to have a U-shapedor C-shaped cross section in FIGS. 17( a)-(c), it may be formed to havea configuration enclosing the entire thermally conductive member 32,that is, annular in cross section.

The thermally conductive member 32 and the metal case 33 ate preferablytightly attached to each other so as not to permit air gaps to interposetherebetween. For example, a silicone adhesive agent (e.g. adhesiveSE9176L produced by Dow Corning Toray Silicone Co., Ltd.) may be appliedbetween the thermally conductive member 32 and the metal case 33.

In addition, the metal case 33 is preferably fixed to the heat sinkmember 5 by means of a thermally conductive adhesive agent, by whichheat of the thermally conductive member 32 is more easily transferred tothe heat sink member 5. Moreover, when the metal case 33 and the heatsink member 5 are integrally formed, heat of the metal case 33 isdirectly transferred to the heat sink member 5. As the foregoingthermally conductive adhesive agent, for example, a thermally conductiveadhesive agent SE4420 produced by Dow Corning Toray Silicone Co., Ltd.may be used.

FIG. 18 is a schematic cross-sectional view of a liquid crystal displaydevice according to another embodiment of the present invention. Thesame elements as in FIG. 15 are denoted by the same reference numerals.Features that are different from those in FIG. 15 are mainly describedbelow.

In this embodiment, the thermally conductive member 32 is in tightattachment to an end surface of the light-guiding plate 3.

Since heat radiated to regions around the LED light source 2 and heat onthe LED-mounting surface side of the mounting board 21 are transferredfrom the thermally conductive member 32 directly to the end surface ofthe light-guiding plate 3, such heat can be transferred to thelight-guiding plate 3. Heat of the LED light source 2 can be transferredthrough the thermally conductive member 32 to the heat sink member 5. Inaddition, heat emitted from the mounting board 21 can be transferredthrough the thermally conductive member 32 interposed between themounting board 21 and the heat sink member 5 to the heat sink member 5.

Here, the thickness of the thermally conductive member 32 at a stagebefore it is interposed between the mounting board 21 and the heat sinkmember 5 (thickness with respect to the thickness direction of themounting board 21) is determined to be slightly greater than thedesigned distance between the mounting board 21 and the heat sink member5 and the designed distance between the mounting board 21 and thelight-guiding plate 3. This ensures that the thermally conductive member32 is securely held between the mounting board 21 and the light-guidingplate 3 and between the mounting board 21 and the heat sink member 5 ina pressure contacted manner. As a result, generation of air gaps can bewell prevented and heat can be dissipated efficiently.

FIG. 19 is a schematic cross-sectional view of a liquid crystal displaydevice according to another embodiment of the present invention. Thesame elements as in FIG. 1 are denoted by the same reference numerals.Features that are different from those in FIG. 1 are mainly describedbelow.

In this embodiment, as shown in FIGS. 19 and 20, the surface(LED-mounting surface) of the mounting board 21 and the light-emittingsurface of the LED container 23 b constituting the LED light source 2are disposed substantially perpendicular to each other.

Accordingly, the light-emitting direction of the LED light source 2 isparallel to the LED-mounting surface of the mounting board 21 as shownin FIG. 20.

In addition, the light-emitting surface and the back surface (thesurface opposite to the light-emitting surface) of the LED light source2 are covered with a thermally conductive member 34.

This thermally conductive member 34 has a configuration includingopening portions 34 a that are open in the lower side for accommodatingthe LED light sources 2 as shown in FIG. 21 so as to surround foursurfaces of the LED light source 2 joined to the mounting board 21except one side surface and the light-emitting surface thereof.

The thermally conductive member 34 is pressed toward the mounting board21 by the upper housing 4. In addition, the thermally conductive member34 is pressed by the upper housing 4 and the heat sink member 5 from theback surface side of the LED light source 2 toward an end surface sideof the light-guiding plate 3.

Accordingly, heat generated from the LED light sources 2 can betransferred to the upper housing 4 and the heat sink member 5 throughthe projected portions 34 b of the thermally conductive member 34present around the LED light sources 2.

As described above, since heat generated at LED light sources 2 iseffectively dissipated to the outside and becomes less likely to bestored in the LED light sources 2 or the mounting board 21, temperaturerise at the LED light sources 2 and regions around them can beeffectively suppressed.

Meanwhile, while the opening portions 34 a of the thermally conductivemember 34 shown in FIG. 21 are provided so as to correspond to theplurality of LED light sources 2, the placement of the mounting board 21on such a thermally conductive member 34 may be carried out by pressfitting with the LED light sources 2 mounted on the mounting board 21being positioned at the opening portions 34 a.

Here, the thickness of the thermally conductive member 34 before it isinterposed between the mounting board 21 and the upper housing 4 ispreferably slightly greater than the designed distance between themounting board 21 and the upper housing 4, and the thickness of theopening portions 34 a are preferably about the same as the mountedthickness of the LED light sources 2.

By setting the thickness of the thermally conductive member 34 as above,the thermally conductive member 34 can be placed in tight attachment tothe LED-mounting surface of the mounting board 21 and a side surface(the side surface between the light-emitting surface and the backsurface that is opposite to the mounting board 21) of the LED lightsource 2.

Here, the thermally conductive member 34 is preferably made of softrubber. Since this allows warpage and irregularities of the mountingboard 21 and the heat sink member 5 to be absorbed, very few air gapsare permitted to interpose between the thermally conductive member 34and the mounting board 21, between the thermally conductive member 34and the heat sink member 5, and between the thermally conductive member34 and the upper housing 4, so that they are tightly attached to eachother in good condition, improving the heat dissipation.

Furthermore, since the thermally conductive member 34 is provided withthe opening portions 34 a for accommodating the LED light sources 2 andthe projected portions 34 b arranged between adjacent opening portions34 a are abutted with the LED-mounting surface of the mounting board 21,light rays other than those directed to the end surface of thelight-guiding plate 3 are blocked or reflected. As a result, leakage oflight can be prevented, and light utilization efficiency can beenhanced.

Meanwhile, since most of the heat of the LED light sources 2 istransferred from the terminal portions 23 c through the metal wiringformed on the mounting board 21, heat dissipation effect is greater whenthe thermally conductive member 34 is brought into contact with themetal wiring of the mounting board 21 and further with the terminalportions 23 c.

Now, a description will be given to an embodiment in which the LED lightsources 2 are mounted on the mounting board 21 in such a way thatthermal conduction from the LED light sources 2 to the mounting board 21is improved.

In this embodiment, as shown in FIG. 6, the LED light source 2 ismounted on a mounting metal film 22 of the mounting board 21 through aheat dissipating bonding material 30 with good heat dissipatingcapability as well as adhesiveness.

The effect of interposing this heat dissipating bonding material 30between the LED light source 2 and the mounting board 21 is as follows.

Usually, the LED light source 2 and the mounting board 21 are onlyconnected at two positions, which are the connection terminal portions23 c, by means of an electrically conductive member or solder.

Accordingly, in conventional cases, heat generated at the LED chip 23 aof the LED light source 2 is transferred from the LED container 23 b tothe mounting board 21 through the connection terminal portions 23 c, andheat other than that is emitted to the ambient air around the LEDcontainer.

In comparison with this, according to the present invention, gaps (airlayers) between the LED container 23 b of the LED light source 2 and themounting board 21 are eliminated to be filled with the heat dissipatingbonding material 30. This allows the heat stored in the LED container 23b to be transferred efficiently to the mounting metal film 22 of themounting board 21 through the heat dissipating bonding material 30. As aresult, the heat can be transferred efficiently to the heat dissipatingmetal film 26 through a plurality of metal via holes 27.

Furthermore, by integrally forming the mounting metal film 22 and themetal film pattern 25, or even when the mounting metal film 22 and themetal film pattern 25 are formed separately, by applying the heatdissipating bonding material 30 so as to cover across the both, heat ofthe LED container 23 b can be effectively transferred to the side of themounting board 21 as well as to the heat dissipating metal film 26through the plurality of via holes 27.

As described so far, owing to the use of the heat dissipating bondingmaterial 30, the formation of the metal via holes 27 penetrating themounting board 21 from the LED-mounting surface to the back surfacethereof, the provision of the mounting metal film 22 and the metal filmpattern 25 on the LED-mounting surface and the heat dissipating metalfilm 26 on the back surface of the mounting board 21 to increase theheat transfer effect of the metal via holes 27, and the use of acopper-based highly thermally conductive material for the mounting metalfilm 22, the heat dissipating metal film 26, the metal film pattern 25and the metal via holes 27, heat of the LED container 23 b of the LEDlight source 2 can be transferred efficiently to the side of the heatdissipating metal film 26 of the mounting board 21, so that temperaturerise around the LED chip 21 a can be suppressed effectively.

This heat dissipating bonding material 30 preferably has an insulatingfunction in addition to the aforementioned heat dissipation andadhesiveness to prevent short circuit between the terminal portions 23 cof the LED light source 2.

The heat dissipating bonding material 30 may be formed so that it isextended from the region in which the mounting metal film 22 is formedto reach the regions in which the metal via holes 27 are formed exceptfor the regions of the metal film 24 to which the terminal portions 23c, 23 c are joined.

In this structure, heat stored in the LED container 23 b of the LEDlight source 2 can be transferred through the heat dissipating bondingmaterial 30 not only to the mounting metal film 22, but also directly tothe metal film 25, as well as to the dissipating metal film 26 on theback surface side of the mounting board 21 through many metal via holes27.

Accordingly, it is possible to efficiently transfer heat stored in theLED container 23 b of the LED light source 2 to the heat dissipatingmetal film 28 of the mounting board 21.

In order to obtain the same effect, the mounting metal film 22 may beextended so as to be formed substantially integrally with the metal filmpattern 25 (in other words, connecting the mounting metal film 22 andthe metal film pattern 25 together).

Another embodiment using a different means instead of the heatdissipating bonding material 30 will be described below.

In the case of a conventional surface mounting type LED light source 2,terminal portions 23 b provided on both sides of the LED light source 2and predetermined wiring connection terminals of the mounting board 21are positioned at predetermined locations and connected to each other bymeans of a solder reflow method or the like.

However, air gaps with poor thermal conductivity tend to be generatedbetween the LED container 23 b accommodating the LED chip 23 a of theLED light source 2 and the mounting board 21.

According to the present invention, an adhesive agent 35 with highfluidity is supplied to the air gaps by a dispenser coating method orthe like.

For example, the LED light source 2 is mounted on the mounting board 21,and the adhesive agent is applied from one side of a LED case to beimpregnated therewith. It is important that this adhesive agent withhigh fluidity is a material with high fluidity that does not corrode themetal wiring and the like.

Because of the high fluidity, the adhesive agent is distributed intogaps between the LED container 23 b and the mounting board 21. As aresult, formation of air gaps such as air bubbles are successfullyprevented, so that the thermal conduction in this part is improved.

Accordingly, heat generated at the LED light source 2 is efficientlytransferred to the mounting board 21 through the adhesive agent and theterminal portions 23 c.

In addition, since mechanical joining between the LED light source 2 andthe mounting board 21 is accomplished not only by the joints of theterminal portions 23 c but also by the adhesive agent 30 providedbetween the LED container 23 b and the mounting board 21, the mechanicaljoining strength between the LED light source 2 and the mounting board21 can be increased, thereby realizing a liquid crystal display devicewith excellent impact resistance.

While specific embodiments of the present invention have been heretoforedescribed, implementation of the present invention is not limited to theforegoing embodiments. For example, in many of the foregoingembodiments, although the light-guiding plate is thicker on the side ofthe end surface in the proximity of the LED light source 2 and thinneron the side of the end surface (the end surface opposite to the endsurface in the proximity of the LED light source 2) apart from the LEDlight source 2, this relationship in thickness between both end surfacesmay be reversed, or the light-guiding plate may be a flat plate memberwhose thickness is the same at the both end surfaces. Also, the sizes inthe depth direction of the side surfaces of the lower side housing whichalso serves as the heat sink member 5 may be the same. In addition,while the heat sink member 5 is exposed at the back surface side of theliquid crystal display device because the heat sink member 5 also servesas the lower side housing, the heat sink member 5 and the lower housingmay be formed as different members separately, or a resin may be moldedand formed only on the surface on the side of the heat sink member 5 tobe exposed so as to conform to the external appearance of the upperhousing 4.

EXAMPLE 1

A thermally conductive sheet (Model No. 5509 of Sumitomo 3M Limited)with heat dissipation properties shown in FIG. 10 was employed for thethermally conductive sheet 31, and a 2 mm thick aluminum was used forthe heat sink member 5, so that the mounting board 21, thermallyconductive sheet 31 and the heat sink member 5 were in surface contactwith each other.

Here, the thermal conductivities of the respective materials used were:0.45 W/(m·K) for glass epoxy used for the mounting board 21, 5 W/ (m·K)for the thermally conductive sheet 31, and 236 W/(m·K) for aluminum forthe heat sink member 5.

Also magnesium or iron may be used for the heat sink member 5. Thethermal conductivity of magnesium is 157 W/(m·K), and the thermalconductivity of iron is 83.5 W/(m·K). In the case of poor heatdissipation, the plate thickness may be increased or a heat dissipatingfin may be provided.

Heat generated together with light emission from the LED light source 2is transferred through the mounting board 21 and the thermallyconductive sheet 31 to the heat sink member 5 to be dissipated. Also theheat is transferred from the lower end surface of the mounting board 21to the heat sink member 5 to be dissipated.

Since the thermal conductivities of the mounting board 21 and thethermally conductive sheet 31 are extremely lower than that of thealuminum of the heat sink member 5, in order to improve heat conduction,reducing the thicknesses of the mounting board 21 and the thermallyconductive sheet 31 possibly to minimum is effective.

A liquid crystal display panel 1 with a display area of 4.7 inches wasused, in which sixteen LED light sources 2 were mounted and aligned onthe mounting board 21. Under room temperature (25° C.), an electriccurrent of 20 mA was applied to the LED light sources 2, andtemperatures around the LED light sources 2 were measured.

As a result, it was revealed that temperatures around the LED lightsources 2 were suppressed to 40° C., and the estimated life of the LEDlight sources could be prolonged up to about 7500 hours. In addition,although the degree was small, an improving tendency was observed in theluminous efficiency of the LED light sources.

On the other hand, when the thermally conductive sheet 31 was excluded,temperatures around the LED light sources reached 44° C., and theestimated life of the LED light sources was no longer than 6600 hours.

The results of the experiment verifies that by improving heat conductionby bringing the thermally conductive sheet 31 into tight attachment tothe mounting board 21 and the heat sink member 5, and therebyefficiently transferring heat generated from the LED light sources tothe heat sink member 5, the heat storage in the LED light sources 2 andthe mounting board 21 can be reduced, and temperature rise at the LEDlight sources and regions around them can be minimized.

EXAMPLE 2

The same temperature measurements as in Example 1 were carried out on asample with a fluid 17 with low fluidity (thermally conductive compound)being applied between the mounting board 21 and the thermally conductivesheet 31 and between the thermally conductive sheet 31 and the heat sinkmember 5.

As the thermally conductive compound, SC102 produced by Dow CorningToray Silicone Co., Ltd. was used, and the mounting board 21, thethermally conductive sheet 31 and the heat sink member 5 were fixed sothat they were in surface contact with each other. The thermallyconductive compound had a thermal conductivity of 0.8 W/(m·K).

The thermally conductive compound is in a clayish condition, whichincludes an oil component with high viscosity mixed with ceramic fineparticles with high thermal conductivity, and the oil component conformsto minute irregularities formed on the surfaces of the heat sink member5 and the mounting board 21, as well as good heat conduction is achievedthrough the ceramic particles with high thermal conductivity.

A liquid crystal display panel 1 with a display area of 4.7 inches wasused, in which sixteen LED light sources 2 were mounted and aligned onthe mounting board 21. Under room temperature (25° C.), an electriccurrent of 20 mA was applied to the LED light sources 2, andtemperatures around the LED light sources 2 were measured.

As a result, it was revealed that temperatures around the LED lightsources 2 were suppressed to 39° C., and the estimated life of the LEDlight sources could be prolonged up to about 7700 hours. In addition,although the degree was small, an improving tendency was observed in theluminous efficiency of the LED light sources.

On the other hand, when the thermally conductive sheet 31 and thethermally conductive compound were excluded, temperatures around the LEDlight sources reached 44° C., and the estimated life of the LED lightsources was no longer than 6600 hours.

The results of the experiment verifies that by interposing the thermallyconductive compound between the thermally conductive sheet 31 and themounting board 21 and between the thermal conductive sheet 31 and theheat sink member 5, the heat conduction from the LED light sources 2 tothe heat sink member 5 can be further improved.

EXAMPLE 3

The same temperature measurements as in Example 1 were carried out, inwhich a thermally conductive member 20 was added to the structure inExample 1.

The same material as the plate-like thermally conductive sheet with heatdissipation properties (Model No. 5509 of Sumitomo 3M Limited) was usedfor the thermally conductive member 20, and the mounting board 21 andthe end surface on the light incident side of the light-guiding plate 3were fixed so that they were brought into surface contact with eachother.

Heat generated together with light emission from the LED light sources 2is transferred through the mounting board 21 and the thermallyconductive member 20 to be transferred also to the light-guiding plate3. Accordingly, heat transferred from the mounting board 21 to the heatsink member 5 is dissipated mainly through three routes on theLED-mounting surface side, the back surface side and the lower endsurface side of the mounting board 21.

A liquid crystal display panel 1 with a display area of 4.7 inches wasused, in which sixteen LED light sources 2 were mounted and aligned onthe mounting board 21. Under room temperature (25° C.), an electriccurrent of 20 mA was applied to the LED light sources 2, andtemperatures around the LED light sources 2 were measured.

As a result, it was revealed that temperatures around the LED lightsources 2 were suppressed to 36° C., and the estimated life of the LEDlight sources could be prolonged up to about 8500 hours. In addition,although the degree was small, an improving tendency was observed in theluminous efficiency of the LED light sources.

On the other hand, when the thermally conductive member 20 and thethermally conductive sheet 31 were excluded, temperatures around the LEDlight sources reached 44° C., and the estimated life of the LED lightsources was no longer than 6600 hours.

The results of the experiment verifies that by bringing the thermallyconductive member 20 and the thermally conductive sheet 31 into tightattachment to the mounting board 21 and the heat sink member 5, the heatconduction was improved, and heat generated from the LED light sourcescan be efficiently transferred to the light-guiding plate 3 and the heatsink member 5.

EXAMPLE 4

The same temperature measurements were carried out using the thermallyconductive member 32 shown in FIG. 16(a) (Model No. 5509 of Sumitomo 3MLimited), in which the mounting board 21 and the thermally conductivemember 32, and the thermally conductive member 32 and the heat sinkmember 5 were fixed so that they were brought into surface contact witheach other, respectively.

A liquid crystal display panel 1 with a display area of 4.7 inches wasused, in which eighteen LED light sources 2 were mounted and aligned onthe mounting board 21. Under room temperature (25° C.), an electriccurrent of 20 mA was applied to the LED light sources 2, andtemperatures around the LED light sources 2 were measured.

As a result, it was revealed that temperatures around the LED lightsources 2 were suppressed to 34° C., and the estimated life of the LEDlight source array could be prolonged up to about 9000 hours. Inaddition, although the degree was small, an improving tendency wasobserved in the luminous efficiency of the LED light source array.

On the other hand, when the thermally conductive member 32 was excluded,temperatures around the LED light sources reached 45° C., and theestimated life of the LED light source array was no longer than 6400hours.

The results of the experiment verifies that by bringing the thermallyconductive member 32 shown in FIG. 16( a) into tight attachment to themounting board 21, the heat sink member 5 and the light-guiding plate 3,the heat conduction can be further improved.

In addition, because the thermally conductive member 32 is held withinthe heat sink member 5, the mounting board 21 can be maintained at thepredetermined position with high stability, and moreover, even whenimpact is applied from the outside of the housing 6, the thermallyconductive member 32 is capable of absorbing the impact. For thisreason, a liquid crystal display device with high reliability in whichthe LED light sources 2 is not displaced or broken can be produced.

EXAMPLE 5

The same temperature measurements as in Example 1 were carried out on aliquid crystal display device in which, as shown in FIG. 19, the LEDlight sources 2 were mounted on the mounting board 21 so that theLED-mounting surface of the mounting board 21 and the light-emittingsurface of the LED light sources 2 were generally in parallel to eachother, and one of the side surfaces of each of the LED containers 23 bof the LED light sources 2 was mounted on the mounting board 21 as aLED-mounting surface.

A plate-like rubber sheet with heat dissipation properties (Model No.5509 of Sumitomo 3M Limited) was used as the thermally conductive member34, and it was fixed so as to be in surface contact with the LED lightsources 2, the heat sink member 5 and the upper side housing 4.

A part of heat generated from the LED light source 2 together with lightemission is transferred through the LED container 23 b and the thermallyconductive member 34 to be dissipated from the upper side housing 4 aswell as dissipated from the side surface side of the heat sink member 5.

A liquid crystal display panel 1 with a display area of 4.7 inches wasused, in which sixteen LED light sources 2 were mounted and aligned onthe mounting board 21. Under room temperature (25° C.), an electriccurrent of 20 mA was applied to the LED light sources 2, andtemperatures around the LED light sources 2 within the backlight weremeasured. As a result, it was revealed that temperatures around the LEDlight sources 2 were suppressed to 36° C., and the estimated life of theLED light sources 2 could be prolonged up to about 8500 hours. Inaddition, although the degree was small, an improving tendency wasobserved in the luminous efficiency of the LED light sources 2.

On the other hand, when the thermally conductive member 34 was excluded,temperatures around the LED light sources reached 44° C., and theestimated life of the LED light sources 2 was no longer than 6600 hours.

The results of the experiment verifies that heat generated from LEDlight sources 2 can be efficiently transferred to the upper housing 4and the heat sink member 5 through the thermally conductive member 34.

EXAMPLE 6

As shown in FIG. 6, a 0.1 mm thick mounting board 21 whose both surfaceswere provided with metal films 22, 26, a metal film pattern 25 and adriving metal wiring 24 was prepared. A 35 μm thick copper foil was usedas the metal films. Through holes of 0.2 mm in diameter were provided asmetal via holes 27, and inner peripheral walls of the through holes wereplated with 25 μm thick copper.

A heat dissipating metal film 26 for the mounting board 21 was formed toa thickness of 35 μm to 60 μm that was larger than those of other filmsincluding the mounting metal film 22 and the metal film pattern 25 so asto facilitate heat conduction and dispersion. The surfaces of the metalfilms made of copper were coated with a solder film 28 with a thicknessof about 20 μm. This improves not only the above described heatdissipating effect but also facilitates mounting of the LED lightsources 2 and driving parts thereof on the mounting board 21 bysoldering, and prevents the surfaces of the copper parts from oxidation,discoloring and corrosion.

Since the thermal conductivity of the mounting board 21 is extremelysmaller than those of the metal materials used for the mounting metalfilm 22, the heat dissipating metal film 26, the metal film pattern 25and the heat sink member 5, in order to improve the heat conduction ofthe heat sink member 5, reducing the thickness of the mounting boardpossibly to minimum is effective. A thin glass epoxy substrate was usedfor reliable insulation and cost reduction.

A 2 mm thick rectangular plate made of aluminum was used as the heatsink member 5, which was bent to have an L-shaped cross section so as tobe in surface contact with the heat dissipating metal film 26 of themounting board 21 and fixed to the mounting board 21 with screws. Here,thermal conductivities of the materials used were: 0.45 W/(m·K) for themounting substrate (base body of the mounting board) made of glassfiber-based epoxy resin, 403 W/(m·K) for the copper, 236 W/(m·K) for thealuminum, 62.1 W/(m·K) for the solder, and 0.92 W(m·K) for the heatdissipating bonding material.

Heat generated together with light emission at the LED chip 23 a of theLED light source 2 is transferred through the heat dissipating bondingmaterial 30 filled between the LED container 23 b of the LED lightsource 2 and the mounting board 21.

As the heat dissipating bonding material 30, a thermally conductiveadhesive agent (SE4420 produced by Dow Corning Toray Silicone Co., Ltd.)was used.

A 5.7 inch rectangular liquid crystal panel 1 was used as the liquidcrystal display device, in which five LED light sources 2 were mountedlinearly on the mounting board 21. An electric current of 250 mA wasapplied to each of the LED light sources 2, and then temperature rise atthe LED-mounting surface of the mounting board 21 was measured.

As a result, temperature rise could be suppressed to 25° C. or below,and temperature rise at the back surface side could be suppressed to 18°C. or below. The decrease in luminance efficiency as compared to theluminance efficiency at room temperature of the LED light sourceincluding the LED light sources 2 was as small as about 2%, and a brightdisplay was realized.

On the other hand, in a liquid crystal display device having an LEDbacklight, temperature rise at the mounting board, in particular, atregions around the LED light source was great: the temperature rose to50° C. or more on the LED-mounting surface side of the mounting board,and the luminance efficiency of the LED light source decreased by 4% ormore. In addition, when the environmental temperature under which theliquid crystal display device was used was raised from room temperature(25° C.) to 70° C., the temperature of the mounting board reached 120□or more, which was a condition under which damage to the LEDlight-emitting device could be anticipated.

The results of the experiment verifies that owing to the LED lightsource 2 mounting arrangement (interposing the heat dissipating bondingmaterial 30), and various arrangements including the mounting metal film22 of the mounting board 21, the heat dissipating metal film 26, themetal film pattern 25 and the metal via hole conductors 27, the heatconduction can be improved and heat generated from the LED light sources2 can be efficiently transferred to the heat sink member 5.

EXAMPLE 7

The same temperature measurements as in Example 6 were carried out usinga silicone adhesive agent instead of the heat dissipating bondingmaterial 30. In addition, the thermally conductive member 32 as inExample 4 was also used.

As the adhesive agent (bonding material), SE9176L produced by DowCorning Toray Silicone Co., Ltd. was used.

While the thermal conductivity of air is 0.017 W/(m·K), the citedadhesive agent has a greater heat conduction effect as compared withair.

It is preferred that insulative fine particulate material or the like ismixed into the adhesive agent so as to further improve the thermalconductivity as long as it allows the adhesive agent to penetraterapidly into gaps between the LED container 23 b and the mounting board21 and to eliminate air.

A liquid crystal display panel 1 with a display area of 4.7 inches wasused, in which sixteen LED light sources 2 were mounted and aligned onthe mounting board 21. Under room temperature (25° C.), an electriccurrent of 20 mA was applied to the LED light sources 2, andtemperatures around the LED light sources 2 within the backlight weremeasured.

As a result, it was revealed that temperatures around the LED lightsources 2 were suppressed to 40° C., and the estimated life of the LEDlight sources 2 could be prolonged up to about 7500 hours. In addition,although the degree was small, an improving tendency was observed in theluminous efficiency of the LED light sources 2.

On the other hand, when the adhesive agent and the thermally conductivemember 32 were excluded, temperatures around the LED light sourcesreached 44° C., and the estimated life of the LED light sources 2 was nolonger than 6600 hours.

The results of the experiment verifies that by applying the adhesiveagent 35 into gaps between the LED containers 23 b of the LED lightsources 2 and the mounting board 21 so that the thermally conductivemember 32 is in tight attachment to the mounting board 21 and the heatsink member 5, the heat conduction can be improved, and thereby heatgenerated from LED light sources 2 can be efficiently transferred to theheat sink member 5.

1-25. (canceled)
 26. A light source device comprising: a light source; amounting board on which the light source is mounted; a light-guidingplate into which light from the light source is to enter; a heat sinkmember disposed to have a space between the heat sink member and themounting board; and a thermally conductive member in the space.
 27. Thelight source device according to claim 26, wherein the thermallyconductive member is adhered to the heat sink member by an adhesiveagent with high fluidity.
 28. The light source device according to claim26, wherein the thermally conductive member is joined to terminalportions provided in the light sources.
 29. The light source deviceaccording to claim 26, wherein the thermally conductive member is joinedto a metal wiring formed on the mounting board.
 30. The light sourcedevice according to claim 26, wherein the thermally conductive memberincludes a first thermally conductive member for covering a back surfacedisposed on the opposite side of a mounting surface of the mountingboard on which the light sources are mounted, and a second thermallyconductive member for covering the mounting surface of the mountingboard and surfaces of light sources such that at least light-emittingsurfaces of the light sources are exposed.
 31. The light source deviceaccording to claim 30, wherein the second thermally conductive member isdisposed so as to be in tight attachment to the end surface of thelight-guiding plate and the mounting surface of the mounting board. 32.The light source device according to claim 31, wherein the firstthermally conductive member is integral with the second thermallyconductive member.
 33. The light source device according to claim 32,wherein the thermally conductive member further includes a thirdthermally conductive member that covers at least one side surfaces ofthe mounting board and the third thermally conductive member, and thefirst thermally conductive member and the second thermally conductivemember are integral with each other.
 34. The light source deviceaccording to claim 26, wherein the heat sink member is a metal case forholding the light sources and the thermally conductive member.
 35. Thelight source device according to claim 34, wherein the metal case hasopening portions corresponding to the light sources, and the lightsources are connected to the light-guiding plate through the openingportions.
 36. The light source device according to claim 35, furthercomprising a light reflecting means that covers at least a part of thelight-guiding plate and reflects light from the light sources that isincident inside the light-guiding plate.
 37. The light source deviceaccording to claim 36, wherein the reflecting means covers the thermallyconductive member.
 38. The light source device according to claim 26,wherein the thermally conductive member including an extended portionthat covers the mounting surface of the a mounting board, a back surfacedisposed opposite to the mounting surface, and a side surface connectingthe mounting surface to the back surface and the extended portion isconnected to the heat sink member.
 39. The light source device accordingto claim 26, wherein a mounting metal film is formed on the mountingsurface of the mounting board, and the light sources are attached to themounting metal film through a heat dissipating bonding material withgood heat dissipating properties and adhesiveness.
 40. The light sourcedevice according to claim 26, wherein a heat dissipating metal film isformed on a back surface located opposite to the mounting surface of themounting board, and the heat dissipating metal film is connected tometal via holes penetrating between the mounting surface and the backsurface.
 41. The light source device according to claim 26, wherein amounting metal film joined to the light sources and a metal film patternthat is electrically connected to the mounting metal film are formed onthe mounting surface of the mounting board.
 42. The light source deviceaccording to claim 26, wherein an adhesive agent with fluidity is filledinto gaps formed between the light sources and the mounting board.
 43. Aliquid crystal display device comprising: a light source deviceincluding a light source, a mounting board on which the light source aremounted, a light-guiding plate into which light from the light source isto enter, a heat sink member disposed to have a space between the heatsink member and the mounting board, and a thermally conductive member inthe space; and a liquid crystal display panel facing the light-guidingplate of the light source device.